The present invention relates generally to rotary engines, and specifically to rotor and stator airfoils for gas turbine engines and other turbomachinery. In particular, the invention relates to airfoil geometry for blades and vanes subject to high velocity working fluid flow, including transonic flow applications.
Gas turbine engines include a variety of rotary-type internal combustion engines and combustion turbines, with applications in industrial power generation, aviation and transportation. The core of the gas turbine engine typically comprises a compressor, a combustor and a turbine, which are arranged in flow series with an upstream inlet and downstream exhaust. Incoming air is compressed in the compressor and mixed with fuel in the combustor, then ignited to generate hot combustion gas. The turbine generates rotational energy from the hot combustion gas, and cooler, expanded combustion products are exhausted downstream.
The compressor and turbine sections are usually arranged into one or more differentially rotating spools. The spools are further divided into stages, or alternating rows of blades and vanes. The blades and vanes generally have airfoil-shaped cross sections, which are designed to accelerate, turn and compress the working fluid flow, and to generate lift that is converted to rotational energy in the turbine.
In industrial gas turbines, power is delivered via an output shaft coupled to an electrical generator or other load, typically utilizing an external gearbox. Other configurations include turbofan, turboprop, turbojet and turboshaft engines for fixed-wing aircraft and helicopters, and specialized turbine engines for marine and land-based transportation, including naval vessels, trains and armored vehicles.
In turboprop and turboshaft engines the turbine drives a propeller or rotor, typically using a reduction gearbox to control blade speed. Turbojets generate thrust primarily from the exhaust, while turbofans drive a fan to accelerate flow around the engine core. Commercial turbofans are typically ducted, but unducted designs are also known. Some turbofans also utilize a geared drive to provide greater fan speed control, for example to reduce noise and increase engine efficiency, or to increase or decrease specific thrust.
Aviation turbines generally utilize two and three-spool configurations, with a corresponding number of coaxially rotating turbine and compressor sections. In two-spool designs the high pressure turbine drives a high pressure compressor, forming the high pressure spool or high spool. The low spool drives the fan, or a shaft for the rotor or propeller, and may include one or more low pressure compressor stages. Aviation turbines also power auxiliary devices including electrical generators, hydraulic pumps and elements of the environmental control system, for example using bleed air from the compressor or via an accessory gearbox.
In high-bypass turbofans, most of the thrust is generated by the fan. Variable-area nozzle surfaces can be deployed to regulate the bypass pressure and improve fan performance, particularly during takeoff and landing. Low-bypass turbofans provide greater specific thrust but are louder and less fuel efficient, and are more common on military jets and other high-performance aircraft. High-bypass turbofans utilize variable-area nozzle systems to regulate exhaust speed and specific thrust. Afterburner assemblies are typically used on military jets for short-term thrust augmentation.
In general, gas turbine engine performance is constrained by the need for higher compression ratios and combustion temperatures, which increase efficiency and output, versus the cost of increased wear and tear on engine components, including blade and vane airfoils. These tradeoffs are particularly relevant in the turbine stages downstream of the combustor, where gas path temperatures are elevated, and in other turbine and compressor sections subject to high velocity, high pressure working fluid flow, including transonic flow along at least part of the airfoil surface.
Unfortunately, these environments require complex non-linear analysis and modeling techniques, making practical results difficult to accurately predict. High temperature, high pressure and transonic fluid flows also present a combination of engineering and design challenges, emphasizing the need for stress-resistant airfoil geometries that reduce shock-related losses and increase lift and turning efficiency, while improving engine performance and reducing long-term maintenance costs.